A power MOS field effect transistor (MOSFET) may have higher input impedance than a bipolar transistor. Accordingly, the power MOSFET may have a high power gain and a simple gate driving circuit. In addition, since the power MOSFET is a unipolar device, when the device is turned off, there is no time delay due to minority carrier accumulation or recombination. Such a power MOSFET may be applied to a switching mode power supply, a lamp stabilization system, and a motor driving circuit. Usually, a semiconductor device having a DMOS structure using planar diffusion technology is widely used.
Example FIG. 1 illustrates a lateral DMOS device that may include N-well 102 at a single concentration formed on and/or over P-type semiconductor substrate 100, and drain region 104 formed within N-well 102 into which an N-type impurity may be injected at a high concentration. In addition, P-type body region 106 may be formed to have a predetermined distance spaced from the drain region. P+ impurity region 108 and N+ source region 110 may be formed within P-type body region 106. Field insulating film 112 for device separation may be formed on and/or over the surface of semiconductor substrate 100, and gate insulating film 114 and gate electrode 116 may also be formed in a predetermined region on and/or over field insulating film 112. P-type body region 106 and N-well 102 may compose a body diode.
The lateral DMOS device should endure a high drain-source voltage when turned off, while it should enable a lot of current flow between the drain and the source at high speed when turned on. The high drain-source voltage may cause a breakdown in the gate insulating film or at the junction of the body region and the source region. In addition, when a high voltage is continuously applied to the gate insulating film, stress is concentrated on the gate insulating film, which causes breakdown of the gate insulating film. In order to improve the breakdown voltage property of the gate insulating film, the gate insulating film may be relatively thickened. In this case, however, a threshold voltage is increased, which may deteriorate the operation characteristics of the device.
As illustrated in example FIGS. 2 and 3, when an inductor load is driven in a push-pull or bridge structure having DMOS devices m1 and m2, backward conduction Im1, and forward conduction Im2 may occur in the body diode. If large current flows through the body diode, minority carrier accumulation, diode-off delay, and parasitic bipolar junction transistor operation may occur.